High speed sailboat

ABSTRACT

The present invention is an improved downward pulling hydrofoil for use with a sailboat by extending the foil from the windward side of the hull to provide a stabilizing moment equal and opposite to the sail heeling moment. The hydrofoil is provided with a second horizontal foil mounted behind the main holddown foil which second foil is controlled thru a mechanical linkage to keep the main holddown foil tracking in the water for varying wind and sea conditions.

' United States Patent [191 Shutt [451 July 24,1973

[ HIGH SPEED SAILBOAT [76] Inventor: Sidney G. Shutt, 612 Briarwood Dr.,

Brea, Calif.

[22] Filed: June 8, 1972 [21] Appl. No.: 261,076

[52] U.S. Cl 144/39, 114/121, 114/66.5 H [51] Int. Cl B63b 35/00 [58]Field of Search 114/39, 66.5 H, 121-123,

[56] I References Cited FOREIGN PATENTS 0R APPLICATIONS 743,359 9/1966Canada 114/123 Primary Examiner-Milton Buchller Assistant Examiner-D. C.Butler Att0meyEdward Dugas 7] ABSTRACT The present invention is animproved downward pulling hydrofoil for use with a sailboat by extendingthe foil from the windward side of the hull to provide a sta bilizingmoment equal and opposite to the sail heeling moment. The hydrofoil isprovided with a second horizontal foil mounted behind the main holddownfoil which second foil is controlled thru a mechanical linkage to keepthe main holddown foil tracking in the water for varying wind and seaconditions.

8 Claims, 5 Drawing Figures PATENTEUJULZMQH SHEET 2 [IF 2 HIGH SPEEDSAILBOAT BACKGROUND OF THE INVENTION The present invention pertains tothe field of high speed sailboats and more particularly to the field ofsailboats using hydrofoil sections.-

All sailboats provide in their design and construction a means forproducing a counter heeling moment to prevent the sail force fromcapsizing the craft. The conventional approach to achieve a counterheeling moment is to allow the separation between the crafts center ofmass and center of buoyancy to continuously vary to provide an equal andopposite moment to the sail heeling moment. Several variations ofpositioning the center of mass of the boat with respect to the center ofbuoyancy have evolved over many years. The single hull craft, withweighted keel, represents the conventional concept of sailboat rollstability. Improvements have been made to gain a wider mass-buoyancyseparation by increasing the keel weight, by the crew hiking out overthe rail, and by using a trapeze to allow a crew member to hike outbeyond the rail. The multihull crafts achieve greater counter heelingmoments by using greater separation of the mass center and the buoyancycenter, but the basic idea is the same. These crafts have evolved intocatarmarans, out-riggers, trimarans, and proas. All of these can be madelight, with small displacement hulls having low drag. These boats have alarge counter heeling moment which allows the use of larger sails;therefore, very fast boats have been made of these types.

Two or more hulls have the disadvantage that they cost more and althoughtheir drag is low it would be even lower if only one hull having a lowdrag were used. Also, all of the designs presently on the market use amass displaced from the center of buoyancy to achieve stability, thisplaces a limit on the wind velocity the craft can be sailed withoutcapsizing.

In a co-pending U.S. Pat. application, Ser. No. 179,068, filed Sept. 9,1971, entitled HIGH SPEED SAILBOAT; there is disclosed a holddown finwhich is supported from the windward side of a high speed sailboat withthe foil being designed to run just below the waters surface to providea counter force to the heeling moment. The foil disclosed in theco-pending application is satisfactory for a large variation in wind andsea conditions but it has been found that under certain wave conditionsthe holddown foil described in the copending application will tend totear out of the water, thereby eliminating its effectiveness.

The present improved holddown foil is designed to eliminate this tearingout condition for all except the most extreme of conditions.

SUMMARY OF THE INVENTION The present invention is comprised of animproved holddown foil assembly for a sailboat. The foil assembly issupported from the windward side of the boat such that a main horizontalfoil rides below the surface of the water pulling downward with a forcethat is proportional to the angle of incidence of the foil and thesquare of the speed at which the foil is moved thru the water. A secondhorizontal foil is pivotly affixed to a vertical rudder and ismechanically linked to a planing surface such that the position of theplaning surface with respect to the position of the foil assembly abovethe water surface controls the angle of attack of the second horizontalfoil so as to maintain the angle of incidence of the main horizontalfoil at a constant depth below the water surface.

It is therefore an object of the present invention to provide animproved holddown foil for a sailboat.

It is another object of the present invention to provide a holddown foilhaving capability of maintaining itself a fixed distance below the watersurface.

It is another object of the present invention to provide a hydrofoilwith an automatic depth holding feature.

It is a further object of the present invention to provide a hydrofoilhaving a high frequency response for maintaining its depth below thewater surface at a constant.

It is a further object of the present invention to provide a holddownfin for a high speed sailboat which fin has its angle of incidencechanged in proportion to the upward force exerted on the fin and itsdistance below the water surface.

These and other objects of the present invention will become moreapparent when taken in conjunction with the following description anddrawings wherein like characters indicate like parts, and which drawingsform a part of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a prospective view of theimproved holddown foil in place on a high speed sailboat;

FIG. 2 is a top view of the improved holddown foil;

FIG. 3 is a side view, partially sectioned, of the hold down foil ofFIG. '1, in a neutral running position;

FIG. 4 is a side view, partially sectioned, of the holddown foil for anincreasing angle of incidence in response to an upward translation; and

FIG. 5 is a side view, partially sectioned, of the holddown foil for adecreasing angle of incidence in response to a rotation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, theunimaran sailboat 10 uses a single slim hull 11 from which extendsupwards a mast 13 for supporting a sail 12. A centerboard 16 extendsfrom the bottom of the hull to minimize the leeward movement of the hullthrough the water 17. A hiking board 14 provides a seat for the helmsmanand also allows the helmsman to add his weight to the counter heelingforce. Attached to the hiking board 14 is a fin supporting assembly 15which is also connected to the mast 13 by means ofa guy cable 18. Aholddown fin 20 is gimbaled to the supporting assembly 15 and creates adownward force when the hull 11 moves through the I water 17. Thisdownward force is transmitted to the hull through the cable 18 and themast 13. The holddown fin 20 creates the variable force whichcounteracts the varying heeling force. Steering is accomplished with theaid of a rudder 19.

Referring to FIGS. 2 and 3, the foil 20 is gimbaled to the fin supportassembly 15 by means of a shaft 23 and a sleeve 24 which is affixed tothe support assembly 15 to allow the shaft 23 to rotate about the axislabeled B. The shaft 23 is an integral part of an L-shaped member 26. Avertical rudder 22 normally positioned well behind the pivot axis B ispivotly mounted to the L-shaped member 26 at the pivot point labeled A,by means of pins 43. As the rudder 22 moves through the water it isforced to track directly behind the shaft 23.

Connected to the bottom portion of rudder 22 is a forward projecting arm27. Attached to the end of arm 27 is the main horizontal hydrofoilsection 21. The crosssection of the foil is inverted to provide adownward lift, or force F, as the foil is moved thru the water. Aplaning surface 25 which is constructed to operate on the water surfaceis pivotly connected to the L- shaped member 26, at point D, by means oflinkage 28, and pins 29 and 30. A torsional spring 52 connects betweenthe L-shaped member 26 and the linkage 28 to help gravity hold theplaning surface 25 to the back side of waves. The planing surface 25 isnormally positioned in front of the pivot axis B to sense the level ofthe water surface with respect to the holding sleeve 25. The end oflinkage 28 opposite the end connected to the planing surface isconnected by linkages 31 and 32 to a spring 34 and shaft 33. The shaft33 extends downward thru the center of rudder 22 to a lever arm 35. thelever arm 35 is connected to a horizontal stabilizing foil 24, which ispivotly mounted to the rudder 22 by a shaft 42.

Connected at approximately the mid-point on lever arm 35 is a cylinder40, which in combination with a piston 41 forms a dash-pot. The piston41 is connected by a rod 39 to a linkage 38. The linkage 38 is connectedthru linkages 37, 45 and 44 to the linkage 31. One end of linkage 44 ispivotly connected to the rudder 22 at 51. The dash-pot piston 41, underthe influence of the linkages moves approximately 4 times as far as theshaft 33. This provides a mechanical amplification of about 8, of thedash-pot linkage, as compared to the spring linkage of shaft 33 inproducing a change in the angle a for the stabilizer 24. Inservomechanism theory the afore-described linkage produces a leadcompensation to the feedback control system. The main horizontal foil 21is shown inclined downward at an angle 0. When the foil 21 is movedforward at a velocity v in the water it creates a downward force F whichcounteracts the heeling force P pulling upwards on the gimbal sleeve 25.A streamlining shroud 50, shown in dotted lines, protects the linkagesfrom mechanical damage.

In operation the planing surface 25 rides on the water surface,continuously sensing the displacement, y, between the holding gimbal 25and the water surface. A close approximation of Ay is y -y which is theactual input to the linkage. The linkage connects the input Ay to thestabiilizing foil, to control the angle of incidence a of thestabilizing foil, so as to produce a variable force F2 which will rotatethe rudder 22 and the horizontal foil 21 until the inverted foil angleof incidence 0, is at the correct angle to maintain foil force F,, equaland opposite to the pull force P. Operating on a smooth water surface,if the pull force, P, increases the device moves upwards since P isgreater than F,. The planing surface remains on the water surfaceresulting in an increase of Ay which is transmitted through linkage 28to linkage 31. Two parallel linkage paths connect to the stabilizingfoil; to linkage 32, spring 34, shaft 33 to linkage 35, and also tolinkages 45, 37, 38, shaft 39, piston 41, cylinder 40 to linkage 35.Thru the displacement of spring 34 and shaft 33,

0. An increase in 0 results in an increase in F until F is equal to P.

Referring now to FIG. 4, if the water surface increases in height, asfor example thru wave action, causing the planing surface to rise. Thelinkage to the stabilizing foil will decrease or resulting in a downwardforce F2 causing a decrease in 0. A decrease in 0 will reduce F1resulting in P larger than Fl which will cause the entire assembly tomove upward over the incoming wave. If the wave is decreasing in heightthe reverse will occur causing F1 to be larger than P resulting in theassembly moving downward. The assembly will therefore follow the watersurface moving in the direction which tends to make F1 P for variationsin pull force or wave inputs.

Referring to FIG. 5, the stabilizing foil also responds to bodyrotations with the linkage described above. If the rudder assembly 22 isrotated clockwise by a wave disturbance, the linkage changes to producea downward force F2 which rotates the rudder 22 counterclockwise back tothe correct 0. The same linkage, dash-pot and spring provide lead torotation as well as 1 translation. The device is arranged so that thespring and piston 41 and cylinder 40, a change is made in the 6 angle ofincidence of the stabilizing foil, so as to rotate the rudder in thedirection M to thereby stably increase and dash-pot are nominallycentered for all operating values of 0. Inverting the main foil 21results in a stabilized lifting hydrofoil.

While there has been shown what is considered to be the preferredembodiment of the present invention, it will be manifest that manychanges and modifications may be made therein without departing from theessential spirit of the invention. It is intended, therefore, in theannexed claims, to cover all such changes and modifications as fallwithin the true scope of the invention.

I claim:

1. A holddown fin assembly for attachment to a support assembly whichsupport assembly normally projects from the windward side of a sailboathull comprising in combination:

a. a vertical rudder;

b. means for mounting said vertical rudder to said support assembly withat least 2 of freedom such that said rudder normally tracks behind thesupport assembly as it is pulled thru the water;

c. a horizontal holddown fin;

d. means projecting forward from said rudder to support said horizontalfin below the water surface;

e. a planing surface coupled to said vertical rudder, for riding on thewater surface and for providing an indication of the displacement of thesupport assembly with respect to the water surface;

a horizontal stabilizing foil pivotly affixed to said vertical rudder;and

g. means responsive to the indicated displacement of the planing surfacefor controlling the angle of incidence of the stabilizing foil so as tocause the horizontal holddown fin to change its angle of incidence inthe water thereby maintaining the displacement between the supportassembly and the planing surface.

2. The holddown fin assembly of claim 1 wherein said means responsive tothe indicated displacement is comprised of:

a. amplifying linkage for sensing the indicated displacement and forincreasing the indicated displacement;

b. a spring means connected between said amplifying linkage and saidhorizontal stabilizer for rotating said stabilizing foil about saidpivot; and

c. a dash-pot connected between said amplifying linkage and saidhorizontal stabilizer for damping high frequency vibrations in saidstabilizing foil.

3. A holddown fin assembly for attachment to a support assembly whichsupport assembly normally projects from the windward side of a sailboathull comprising in combination:

a. a vertical rudder pivotly affixed to said support assembly;

b. a horizontal holddown fin;

c. means projecting forward from said rudder to support said horizontalfin below the water surface;

(1. a planing surface mechanically linked to said rudder for determiningthe displacement between the support assembly and the water surface;

e. a horizontal stabilizing foil pivotly affixed to said verticalrudder; and

f. means for controlling the angle of said stabilizing foil in responseto said determined displacement for maintaining said displacement at aconstant value.

4. The holddown fin assembly according to claim 3 wherein said means forcontrolling the angle of said stabilizing foil is comprised of:

a. amplifying linkage connected between said planing surface and saidstabilizing foil, for pivoting said horizontal stabilizing foil inresponse to the displacement of said planing surface; and

b. damping means connected between said amplifying linkage and saidhorizontal planing surface for eliminating high frequency vibrations insaid horizontal stabilizing foil.

5. The means for controlling the angle of said stabilizing foilaccording to calim 4 and further comprising:

a. a spring inserted between said amplifying linkage and said horizontalstabilizer for providing a time lag between the displacement sensed bysaid planing surface and the resultant position of the horizontalstabilizing foil.

6. A holddown fin particularly adapted to be mounted from the windwardside of a sailboat to counteract heeling moments, said holddown fincomprising in combination:

a. a horizontal holddown foil;

b. means for pivotly mounting said holddown foil to said sailboat suchthat said foil normally rides below the water surface;

c. a planing means for sensing the displacement between the watersurface and a reference level and for providing a signal proportional tothe sensed displacment;

d. a horizontal stabilizing foil positioned behind said horizontalholddown foil; and

e. servomechanism means for receiving said sensed displacement signaland for controlling the incidence angle of said horizontal stabilizingfoil so as to cause said horizontal holddown foil to change itsincidence angle to be driven deeper or shallower in the water to therebymaintain said sensed displacement signal at a preselected level.

7. The holdown fin according to claim 6 wherein said means for pivotlymounting said holddown foil to said sailboat is comprised of:

a. a vertical rudder gimbaled to said sailboat for two degrees ofangular freedom;

b. a forward projecting member affixed to said vertical rudder forsupporting said horizontal holddown foil substantially below thegimballed point of said vertical rudder, such that the forces acting onsaid horizontal holddown foil are transmitted directly thru the gimbalpoint.

8. The holddown fin according to claim 6 wherein said servomechanismmeans is comprised of:

a. a mechanical linkage connected between said planing means and saidhorizontal stabilizing foil for converting the displacement of saidplaning surface into a corresponding change in the incidence angle ofthe horizontal stabilizing foil.

* l= lk

1. A holddown fin assembly for attachment to a support assembly whichsupport assembly normally projects from the windward side of a sailboathull comprising in combination: a. a vertical rudder; b. means formounting said vertical rudder to said support assembly with at least 2*of freedom such that said rudder normally tracks behind the supportassembly as it is pulled thru the water; c. a horizontal holddown fin;d. means projecting forward from said rudder to support said horizontalfin below the water surface; e. a planing surface coupled to saidvertical rudder, for riding on the water surface and for providing anindication of the displacement of the support assembly with respect tothe water surface; f. a horizontal stabilizing foil pivotly affixed tosaid vertical rudder; and g. means responsive to the indicateddisplacement of the planing surface for controlling the angle ofincidence of the stabilizing foil so as to cause the horizontal holddownfin to change its angle of incidence in the water thereby maintainingthe displacement between the support assembly and the planing surface.2. The holddown fin assembly of claim 1 wherein said means responsive tothe indicated displacement is comprised of: a. amplifying linkage forsensing the indicated displacement and for increasing the indicateddisplacement; b. a spring means connected between said amplifyinglinkage and said horizontal stabilizer for rotating said stabilizingfoil about said pivot; and c. a dash-pot connected between saidamplifying linkage and said horizontal stabilizer for damping highfrequency vibrations in said stabilizing foil.
 3. A holddown finassembly for attachment to a support assembly which support assemblynormally projects from the windward side of a sailboat hull comprisingin combination: a. a vertical rudder pivotly affixed to said supportassembly; b. a horizontal holddown fin; c. means projecting forward fromsaid rudder to support said horizontal fin below the water surface; d. aplaning surface mechanically linked to said rudder for determining thedisplacement between the support assembly and the water surface; e. ahorizontal stabilizing foil pivotly affixed to said vertical rudder; andf. means for controlling the angle of said stabilizing foil in responseto said determined displacement for maintaining said displacement at aconstant value.
 4. The holddown fin assembly according to claim 3wherein said means for controlling the angle of said stabilizing foil iscomprised of: a. amplifying linkage connected between said planingsurface and said stabilizing foil, for pivoting said horizontalstabilizing foil in response to the displacement of said planingsurface; and b. damping means connected between said amplifying linkageand said horizontal planing surface for eliminating high frequencyvibrations in said horizontal stabilizing foil.
 5. The means forcontrolling the angle of said stabilizing foil according to calim 4 andfurther comprising: a. a spring inserted between said amplifying linkageand said horizontal stabilizer for providing a time lag between thedisplacement sensed by Said planing surface and the resultant positionof the horizontal stabilizing foil.
 6. A holddown fin particularlyadapted to be mounted from the windward side of a sailboat to counteractheeling moments, said holddown fin comprising in combination: a. ahorizontal holddown foil; b. means for pivotly mounting said holddownfoil to said sailboat such that said foil normally rides below the watersurface; c. a planing means for sensing the displacement between thewater surface and a reference level and for providing a signalproportional to the sensed displacment; d. a horizontal stabilizing foilpositioned behind said horizontal holddown foil; and e. servomechanismmeans for receiving said sensed displacement signal and for controllingthe incidence angle of said horizontal stabilizing foil so as to causesaid horizontal holddown foil to change its incidence angle to be drivendeeper or shallower in the water to thereby maintain said senseddisplacement signal at a preselected level.
 7. The holdown fin accordingto claim 6 wherein said means for pivotly mounting said holddown foil tosaid sailboat is comprised of: a. a vertical rudder gimbaled to saidsailboat for two degrees of angular freedom; b. a forward projectingmember affixed to said vertical rudder for supporting said horizontalholddown foil substantially below the gimballed point of said verticalrudder, such that the forces acting on said horizontal holddown foil aretransmitted directly thru the gimbal point.
 8. The holddown finaccording to claim 6 wherein said servomechanism means is comprised of:a. a mechanical linkage connected between said planing means and saidhorizontal stabilizing foil for converting the displacement of saidplaning surface into a corresponding change in the incidence angle ofthe horizontal stabilizing foil.